This proposal describes a program designed to develop a new reaction (1,3-diyl-trapping) into a useful synthetic method for the construction of pharmacologically active compounds possessing a tricyclopentanoid or a hydroazulene carbon framework. The reaction has not heretofore been explored as a synthetic tool. However, in recent experiments we have shown that the reaction will be of immense importance as a new general synthesis of complex ring systems. We have shown, for example, that tricyclopentanoid skeletons as exemplified by the antibiotic hirsutic acid and the cytotoxic drug diketocoriolin B can be constructed from two simpler pieces in a single step. The reaction bears some resemblance to the powerful Diels-Alder reaction in that two carbon-carbon bonds are formed at once (i.e., in a single step). However, unlike the Diels-Alder reaction for the facile synthesis of six-membered rings, the diyl trapping reaction holds considerable promise for the facile synthesis of five membered and more complex ring systems. We propose herein to investigate the details of the diyl trapping reaction related to its potential synthetic utility for the construction of tricyclopentanoid carbon frameworks and to apply our findings toward the total synthesis of hirsutic acid and diketocoriolin B. Additionally, we propose to investigate the reaction of 1,3-dienes with 1,3-diyls to ascertain the mode of cycloaddition (1,2- vs. 1,4) and to utilize our results for the construction of hydroazulenic systems as exemplified by guaiol and the cytotoxic pseudoguaianolide helenalin.